Paper sized with cationic vinyl copolymer and process for the manufacture thereof



United States Patent O PAPER SIZED WITH CATIONIC VINYL COPOLY- MER AND PROCESS FOR THE MANUFACTURE THEREGF John H. Daniel, Jr., Old Greenwich, Conn., assignor to American Cyanarnid Company, New York, N.Y., a corporation of Maine No Drawing. Filed May 20, 1958, Ser. No. 736,443

Claims. (Cl. 162-168) The present invention relates to the manufacture of paper of improved water resistance but of substantially unimproved wet strength containing a normally watersoluble cationic linear carbon chain vinyl polymer as more particularly described below. The invention particularly relates to paper of the type described having improved dry strength as the result of the presence of the polymer thereon.

It is known that paper of improved resistance to penetration by water (hereinafter termed sizing) results when a cationic material carrying non-ionic hydrophobic groups and cationic hydrophilic groups is added to aqueous suspensions of papermaking cellulosic fibers prior to the sheeting step. When the wet web is dried, it is found that the resulting paper is well sized; cf. Lundberg U.S. Patent 2,753,372, granted July 3, 1956; Reynolds et al. US. Patent No. 2,772,969, granted December 4, 1956; and Lundberg et a]. US. Patent No. 2,794,737, granted June 4, 1957. It is a principal disadvantage of the papermaking processes disclosed in the patents referred to that the presence of the size on the fibers, in optimum amount, causes a substantial decrease in the dry tensile strength of the paper.

The discovery has now been made that paper having very satisfactory sizing and about normal dry strength can be prepared by forming an aqueous suspension of cellulose papermaking fibers, adding to the suspension a small amount of a water-soluble cationic linear carbon chain vinyl polymer essentially composed of hydrophobic linkages and hydrophilic linkages of the formula [--CH CHX-] wherein X is an organic substituent containing quaternary ammonium groupings, the ratio between said linkages being between about 0.5 :1 and 5:1, sheeting the suspension to form a waterlaid web, and heating the web to dry the same and develop the sizing properties of the polymer thereon.

In addition to being well sized, the paper produced by the process, in preferred embodiments, possesses the following advantages:

(1) The paper has at least normal dry strength, i.e., at least about the same dry strength as rosin sized paper having the same sizing index. In certain instances, the strength of the paper is actually improved as a result of the presence of the polymer thereon.

(2) The sizing is resistant to alkali. As a result, the paper can be used for the packaging of materials such as lime, cement and soap.

(3) The paper may have a nearly neutral or even an alkaline pH. It may thus contain acid-sensitive dyes, pigments and fillers.

In the process, heating the paper in the range of 150 250 F. is necessary to develop the water-repellent properties of the size of the fibers. No reaction of the applied accordingly it has not been possible to identify the precise structural features which cause the sizing elfect. As a result, the paper is most conveniently described in terms of its manner of preparation.

The paper of the present invention is made by the beater addition process, wherein the sizing polymer is added directly to the aqueous suspension of cellulosic papermaking fibers before sheeting. The polymer is preferably added in the form of a dilute solution, preferably aqueous, and is incorporated with the suspension at any convenient point ahead of the wire, a few moments being allowed during which the polymer is substantially adsorbed by the fibers.

The polymer is added in amount between about 0.1% and 5% based on the dry weight of the fibers, depending on the particular amount of sizing desired. A perceptible amount of sizing is generally obtained in the lower part of the range, and we have found that the water resistance imparted per increment of sizing agent added generally falls oif when the weight of sizing agent added is more than about 2%3% of the dry deight of the fibers. Accordingly, the range of 0.3 %3% is regarded as the practical range. In this range, it is possible to produce paper having about the same resistance to penetration by water as ordinary rosin size and having significantly better dry strength.

The paper of the present invention possesses negligible wet strength. The paper therefore can be repulped in ordinary beater equipment without treatment with steam jets or chemicals.

The polymers of the present invention are prepared by copolymerizing two or more vinyl monomers which together form a water-soluble cationic linear carbon chain polymer predominantly composed of hydrophobic linkages and hydrophilic linkages of the formula -CH CHX wherein X is an organic substituent containing at least one quaternary ammonium group each. The monomer supplying the first linkage is vinylidene chloride,

As the vinyl compound contributing the second linkage there is used a vinyl tertiary amine or a vinyl compound carrying a quaternizable halogen atom. Examples of suitable vinyl tertiary amines are the vinyl pyridines, vinyl quinoline, N,N-dimethyl-p-vinyl aniline, N (dimethylaminopropyl) acrylamide, diethylaminoethyl acrylate and the corresponding methacrylate. Such materials may be quaternized by reaction with benzyl chloride, dimethyl sulfate, or methyl chloride. Examples of suitable vinyl compounds carrying a quaternizable halogen atom are vinyl chloroacetate, p-chloromethylstyrene, and chloroethyl acrylate. Such compound may be quaternized by reaction with pyridine, quinoline, trimethylamine or, in general, any water-soluble tertiary amine.

The polymers used in the process of the present invention are water-soluble, that is, they have a solubility such that they can be readily dispersed to form a pumpable aqueous solution containing at least 10% resin solids by weight. In these polymers the dichloroethylene,

linkage is the hydrophobic linkage and the proportion thereof which may be present depends in each instance on the solubilizing effect imparted by the hydrophilic linkages carrying quaternary ammonium groupings. In the case of highly water-soluble (hydrophilic) linkages,

a comparatively large number of the dichloroethylene' Patented Feb. 20, 1962 3 linkages may be present. The ratio between these linkages and the hydrophilic linkages may be as high as about 3:1 or 1. With less hydrophilic quaternary ammonium linkages the ratio of vinylidene chloride should be de' creased, but the ratio of 0511 represents about the least amount of the dichloroethylene linkage which will give useful sizing. The optimum polymer is easily determined by laboratory trial, the preferred polymers sufiiciently soluble to form aqueous solution at C. yet sufficiently hydrophobic so that when cured on the fibers, they impart substantial Water-resistance thereto.

It is within the scope of the invention to employ as components contributing cationic properties water-soluble vinyl monomers containing more than one tertiary nitrogen atom, e.g., vinyl pyrazine. Only sufiicient of the'tertiary nitrogens therein need be quaternized to provide the desired solubility.

The present invention includes the use of polymers containing linkages other than those specified above, and suitable polymers may be prepared by interpolymerizing the vinylidene chloride and the vinyl quaternizable component in the presence of a minor amount of other vinyl compounds copolymerizable therewith, for example, styrene, p-methylstyrene, ethyl acrylate, methacrylonitrile, acrylamide, and mixtures thereof. The polymers employed in the present invention are thus predominantly composed of the linkages supplied by the vinylidene chloride and the vinyl quaternizable component.

The polymerization reaction is performed in any convenient way. Preferably, the monomers are reacted at 50-100 C. using a solvent such as benzene in the presence of an azo or peroxide catalyst, after which unreacted monomer and solvent are advantageously removed.

Thepolymers, as produced, are generally the chlorides of strong organic bases. They may be dissolved in water to form an aqueous solution of convenient resin solids content so as to facilitate pumping and metering. Solutions having a solids content in the range of 3%-10% are convenient in this regard. The polymers dissolve very slowly in'plain water, 12 hours of stirring being not unusual. The time can be greatly decreased by first adding a small amount of acetone, methanol, or dimethyl formamide to the polymer to open up its structure and increase its surface, and then adding the water.

The pH of papermaking fibrous cellulose suspensions is generally in the range 4.5-8.5. Since polymers of the present invention are well adsorbed over this range, adjustment of the pH is not necessary.

The polymer may be added to the papermaking fiber suspension in conjunction with materials heretofore used in the manufacture of paper such as starch, locust bean gum, ultramarine blue, titanium dioxide, phthalocyanine blue, calcium carbonate, papermakers clay, and perfumes. In general, best results are obtained by postponing addition of the sizing polymer until addition of the strengthening agents, pigments, fillers, etc., is complete.

The paper of the present invention develops its dry strength after brief heating at elevated temperatures, preferably in excess of 150 F. This development takes place spontaneously as the paper is dried in customary manner for /2 to 3 minutes on steam-heated rolls in the range of 190-250 F. V

The invention will be further described by reference to I the examples. These examples illustrate specific embodi-.

ments of the invention and are not .to be construed in limitation thereof. Parts are by weight unless otherwise stated.

' Example 1 vinyl-pyridine was prepared with the following raw ma- 4 terials: 10.0 g. vinylidene chloride (freshly distilled); 5.0 g. Z-methyl-5-vinyl-pyridine (distilled); and 0.015 g. azobisisobutyronitrile initiator. These raw materials were charged to a test tube that was sealed under a nitrogen 5 atmosphere. The tube was heated at 70 for five days, at the end of this period the charge had become very viscous indicating some polymerization to have taken place. Polymerization was stopped by breaking the tube, dissolving the contents in 50 ml. of dioxane and precip- 19 itating the copolymer in approximately 300 ml. of nhexane. The gummy precipitate was dried in a forced draft oven at 70 C. By chlorine analysis it was found that the polymer was composed of CH CCl and linkages in 8.7210 molar ratio.

A part of the polymer was dissolved in dioxane and quaternized by heating at 100 C. for four hours with benzyl chloride in 20% stoichiometric excess. The prodnot was dissolved in water to form a 5% by weight solution.

The product was tested by addition to a neutral bleached 60%:40% sulfite:soda pulp at a consistency of 0.6%, stirring gently for 5 minutes without adjustment of pH, forming the pulp into handsheets at -50 lb. basis weight (25" x 40"/500) on a Nash handsheet machine, drying the sheets for one minute at 240 F. and testing the sheets for dry strength and sizing after conditioning for 24 hours at 73 F. and relative humidity.

Results are as follows:

1 Viavli lene chlo"i 1e.

2 2-rn tivl-5-vinylpvri line, q'laternizei with benzyl chloride.

3 Polymer solids, based on dry weight of fibers.

4 Currier, slack scale.

5 Burst (Mujlzn). 50 The results show the polymer gave good sizing and actually improved the dry strength of the paper. From experience it is known that paper of 45 sec. water resistance produced by beater addition of rosin size and alum to the pulp used in the above test would yield-a Mullen dry strength burst value of about 18 1b.

Example 2 The procedure of Example '1 was repeated except that vinyl chloroacetate was used in place of the methyl vinyl 0 pyridine, and pyridine was used as the quaternizing agent. 5 gm. of vinylidene chloride and 10 gm. of vinyl chloroacetate, each freshly distilled, together with 0.015 gm. of azobisbutryonitrile as initiator were charged into a test tube which was sealed under nitrogen and heated at C. for 21 hours. The tube was opened and unreacted monomer removed by heating at 70 C. under vacuum. The product (8 gm.) was dissolved in dioxane and precipitated in pure form in methanol. The methanol was evaporated 01f under vacuum at 70 C.- and 70 quaternization carried out by dissolving 3 gm. of the product in 15 ml. of dioxane containing 2 gm. of pyridine and heating the mixture at C. for30 minutes. The product was then dissolved in water to give a 1% solution. The product was tested by the method of Example 1 7 using a difierent batch of pulp, with results as follows.

Copolymer Dry Strength 1 Sizing 1 Run No. (See) VG, VGAQ, Percent (Lb.) Percent M015 M015 Added 1 Incr.

1 N one 22. O 2 11. 6 10 0. 5 13 26. 0 18. 2 3 11. 6 l0 1. 0 50 29 31. 7

1 See table, Example 1. 3 Vinyl ehloroacetate, quaternized with pyridine.

I claim:

1. Process for the manufacture of sized paper of about normal dry strength, which comprises forming an aqueous suspension of cellulosic papermaking fibers, adding to said suspension an efiective amount as sizing agent, between about 0.1% and 5%, based on the dry weight of said fibers, of an aqnous solution of a water-soluble cationic linear carbon chain vinyl polymer predominantly composed of hydrophobic linkages and hydrophilic linkages of the formula CH CHX wherein X is an organic substituent containing one quaternary ammonium grouping, the ratio between said linkages being between about 05:1 and 5:1, sheeting the suspension to form a waterlaid web, and heating said'web at F.-250 F. to dry the same and develop the sizing properties of the polymer thereon.

2. A process according to claim 1 wherein the aqueous suspension has a pH of between 4.5 and 8.5 during addition of the polymer.

3. A process according to claim 1 wherein the polymer is a quaternized vinylidene chloridewinyl chloroacetate copolymer.

4. A process according to claim 1 wherein the polymer is a quaternized vinylidene chloride:2-methyl-5-vinylpyridine copolymer.

5. Paper prepared according to the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,765,228 Jordon Oct. 2, 1956 2,765,229 McLauglin Oct. 2, 1956 2,794,737 Lundberg et al. June 4, 1957 2,795,545 Gluesenkamp June 11, 1957 2,806,019 Lane Sept. 10, 1957 

1. PROCESS FOR THE MANUFACTURE OF SIZED PAPER OF ABOUT NORMAL DRY STRENGTH, WHICH COMPRISES FORMING AN AQUEOUS SUSPENSION OF CELLULOSIC PAPERMAKING FIBERS, ADDING TO SAID SUSPENSION AN EFFECTIVE AMOUNT AS SIZING AGENT, BETWEEN ABOUT 0.1% AND 5%, BASED ON THE DRY WEIGHT OF SAID FIBERS, OF AN AQUEOUS SOLUTION OF A WATER-SOLUBLE CATIONIC LINEAR CARBON CHAIN VINYL POLYMER PREDOMINANTLY COMPOSED OF HYDROPHOBIC 